diff --git a/libImaging/Convert.c b/libImaging/Convert.c
index 46a6cfb72..3d9119c7f 100644
--- a/libImaging/Convert.c
+++ b/libImaging/Convert.c
@@ -49,6 +49,12 @@
 #define L(rgb)\
     ((INT32) (rgb)[0]*299 + (INT32) (rgb)[1]*587 + (INT32) (rgb)[2]*114)
 
+#ifndef round
+double round(double x) {
+  return floor(x+0.5);
+}
+#endif
+
 /* ------------------- */
 /* 1 (bit) conversions */
 /* ------------------- */